Submitted to: Phytopathology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/5/2002
Publication Date: 10/1/2002
Citation: Sanogo, S., Pomella, P.K., Hebbar, P.K., Bailey, B.A., Costa, J.C., Samuels, G.J., Lumsden, R.D. 2002. Production and germination of conidia by trichoderma stromaticum, a mycoparasite of crinipellis perniciosa on cocao. Phytopathology. 92:1032-1037. Interpretive Summary: The industry involved in production of processed chocolates is a major purchaser of United States agricultural commodities including various flours, sugars, and nuts along with milk, peanuts and other products. Chocolate is produced from the seed of cacao (Theobroma cacao), a tree crop that is under intense pressure around the world from disease and insect pest. A major constraint on cacao in South and Central America is the disease caused by Crinipelis perniciosa, commonly called witches' broom. In Brazil alone, a Cacao seed production was reduced more than 70 percent due to the disease. We are developing biological control measures for the disease using the mycoparasite Trichoderma stromaticum. This study defines the environmental conditions under which T. stromaticum will proliferate and spread once applied to infected cacao tissue. When the humidity is high (100 percent) T. stromaticum germinates and sporulates at 20 and 25 C but not at 15 or 30 C. Under optimum conditions, T. stromaticum prevents growth of C. perniciosa in diseased tissue. This information will allow optimization of disease control strategies that can be used by cacao farmers in areas where witches' broom limits yield of cacao. By developing innovative disease control measures, we can assure the chocolate industry and consumers alike of the cacao seed supplies required to produce the chocolate products for which we are accustomed.
Technical Abstract: Growth characteristics of the the fungus Trichoderma stromaticum, a mycoparasite on the mycelium and fruiting bodies of Crinipellis perniciosa, the causal agent of witches' broom disease of cacao, were evaluated under controlled-environment conditions. The ability of T. stromaticum to produce conidia and germinate on dry brooms was evaluated under three constant temperatures (20, 25, and 30oC) and two constant relative humidity (75 and 100 percent). At a relative humidity of 100 percent and incubation temperatures of 20 and 25oC, T. stromaticum produced abundant conidia on the brooms, but none at 30oC. Sporulation of T. stromaticum was not observed at 75 percent relative humidity at any temperature. At 100 percent relative humidity and at 20 and 25oC, treatment of brooms with T. stromaticum completely eliminated C. perniciosa within 7 days. In contrast, at temperature of 30oC, treatment with T. stromaticum had no effect on the pathogen in brooms maintained at either 75 or 100 percent relative humidity. Mycelium of C. perniciosa grew from brooms at all temperatures at 100 percent relative humidity. Conidia germinated on broom tissue, approximating 80percent at temperatures from 20 to 30oC. Results suggest that applying T. stromaticum during periods of high relative humidity when air temperature is lower than 30oC may enhance the establishment of this mycoparasite in cacao plantations.